Substance use disorder (SUD) is a devastating psychopathology that is without FDA-approved drug therapies. One promising target for pharmacological intervention are CB2 cannabinoid receptors (CB2R). Previous studies have demonstrated that CB2R agonists reduce intravenous self-administration (SA) of cocaine and inhibit cocaine-induced hyperlocomotion. Since CB2R agonists have very few overt behavioral effects, they represent a promising new avenue for the treatment of SUD. Unfortunately, a lack of good experimental tools for their study inhibits further progress in uncovering the potential fo manipulation of CB2R signaling to treat SUDs. We have recently developed a transgenic mouse in which CB2R expression is coupled to eGFP expression and the CB2R gene is floxed, thus can be conditionally deleted (CB2Rtg). This mouse model allows for enhanced detection and enables conditional deletion of the CB2R. Exposure to cocaine is accompanied by microglial activation and reduced microglial activation is associated with reduced cocaine seeking. Microglia express CB2R, which is increased upon microglial activation. Microglial CB2R promote a neuroprotective phenotype, including suppressed release of pro-inflammatory cytokines. Recent studies also demonstrate that CB2R are expressed in DA neurons and function to inhibit DA release. We will test two hypotheses with the experiments in this proposal: that chronic cocaine exposure increases expression of microglial CB2R and that CB2R agonists act via microglial and DA neuronal CB2R to reduce cocaine SA. We will test these hypotheses with two aims. In aim one, we will use the eGFP reporter feature of the CB2Rtg to determine the effects of cocaine on CB2R expression. In aim two, we will use the floxed feature of the CB2Rtg to specifically delete CB2R from microglia and DA neurons; then apply a subtraction approach to explore the cellular site of action of CB2R agonists to reduce locomotor activity and cocaine SA. Successful completion of these studies will impact understanding of the effects of cocaine on neuroinflammation and CB2R expression; and the roles of CB2R in regulating cocaine intake through clarification of the cell types(s) that are involved in the inhibitory actions of CB2R agonists. We will also establish conditional CB2R-/- mouse lines for further studies of the role of this very interesting receptor in brain function. Thus, these studies will impact mechanistic examination of cocaine effects on the brain and provide important new tools for the study of the CB2R in the brain.